UK Financial Investments, which looks after the bailed-out banks on behalf of taxpayers, has produced the first real analysis on how much money might be made on Northern Rock and Bradford & Bingley. It reckons that the "wholly owned" businesses will bring in between £95bn and £97bn – at least £33bn more than was put in.

As always there is a snag. It could take another 15 years for those sums of money to flow back to the exchequer.

On Northern Rock, some £46bn to £48bn could be brought in to repay the £36.8bn of taxpayer money pumped into the bank. On B&B the profit could be as high as £22bn, based on projections that the government will get back £49bn after putting in £27bn during the dark days after Lehman Brothers collapsed in September 2008.

The Northern Rock calculation includes the £400m loss made on the sale of the "good" part of the Newcastle-based lender to Virgin Money at the end of last year. The profit will come from the "bad" bank – Northern Rock Asset Management – as it repays £47bn in the coming 10 to 15 years.

UKFI justifies the £977m sale to Virgin Money, despite it being made at a loss, by arguing (as the table shows) that it was the best value it could get against alternatives such as an immediate share sale through an initial public offering (£495m), a remutualisation (£437m) and a run off (£625m) or an IPO next year (£735m).

While the headline figure on the Virgin sale was £747m, UKFI has based its calculations on projections by its advisers at Deutsche Bank that taxpayers will eventually get between £863m and £977m. Deutsche Bank sent out 24 information memorandums for the sale, including 10 private firms and four mutuals. In the end, none of the mutuals made a bid for the Rock.

UKFI also reveals the fees it racked up: £3.2m. Some £1.8m went to Deutsche Bank which offered a cut price service, according to UKFI. It reckoned some of the 18 other banks that pitched for the mandate were charging up to £7m. Lawyers Freshfields got £765,000, Deloitte £486,000 and a range of others, including PR advisers Maitland, shared £138,000.

UKFI has every need to justify the sale to Virgin Money as the National Audit Office is conducting its own assessment. Whatever the NAO eventually concludes, one thing will be indisputable – that the nationalisation of the banks is anything but the "temporary public ownership" that was promised by the then-chancellor Alistair Darling.